56 Glass-Technology International 3/2014

I G T E C H N O L O G Y

Lightweightglazing units

FOR ARCHITECTURAL

PURPOSESSet against the background of rising requirements on the energy performance of buildings, there is currently an ongoing trend toward thermal triple-glazing. Although this technology is highly efficient, the glass industry is now working on lighter alternatives to counteract the heavy weights that are involved.

As an individual element, vacuum-

insulated glass is less than 1 cm in thickness.

Innovative edge seal technologies are to facilitate the use of float glass, single-sheet safety glass

and laminated safety glass, as well as the

application of nearly all standard coatings.

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Improving the energy performance of win-dows and façades con-

tinues to be one of the cen-tral challenges in modern architecture. As well as op-timising frame sections, a major role is played by the efficiency of the thermal glass that is used for this purpose. Thermal double-glazing has been proving its worth for several deca-des now. By applying hi-ghly efficient functional co-atings and using thermally optimised warm edge spa-cer systems, the relevant Ug value of a glazing unit – so crucial for thermal insulation performance – has been reduced to 1.0 W/m2K with argon-filled glazing. Moreover, a low-emissivity coat is added on the indoor side of a unit, so that the latest products now have values as low as 0.9 W/m2K.

THERMAL TRIPLE-GLAZING IS NOW STATE-OF-THE-ARTYet thermal double-glazing still cannot achieve the same excellent insulating effect as thermal triple-glazing, where the relevant values are now as low as 0.5 W/m2K. This type of glass has the best level of perfor-mance and is currently sta-te-of-the-art in traditional thermal glass applications. Its excellent insulating ef-fect has led to an increased use of triple glazing in buil-dings, as it can best satisfy today’s rising requirements on energy performance. Germany, in particular, has seen substantial growth in this segment. In just four years the market share has increased from about ten to over 60 per cent, and the trend is rising. At the same time there is a tendency to-wards bigger glazing units.

This trend is supported by ongoing developments in manufacturing techno-logies, which now permit the serial manufacturing of very large, high-precision double- and triple-glazing units.

HEAVYWEIGHT GLASS CAN CAUSE PROBLEMSHowever, there is a snag in this trend towards large panels and triple-glazing. If the glass is too heavy, glaziers can easily come to the limits of their strength. Thermal glass with a triple-glazing structure and the usual thickness of 4 millimetres is about one third heavier than double-glazing. As a result, the weight of a glass panel of one square metre in size increases from 20 to 30 ki-los, and a panel that weighs several hundred kilograms

can often only be installed with the help of technical equipment. This leads to a substantial rise in instal-lation costs. Moreover, heavy glass panels make it necessary to develop new handling solutions for the manufacturing process, while also driving up the cost of transport. Another area that is coming to its limits, despite intensive development, concerns the required heavy-duty hinges. For several years now, research institutes and glazing companies have been working with glass machinery manufac-turers on possible remedies in the form of alternative products with similar or better energetic properties, but less weight. The focus is, in particular, on thin units, transparent film and plastic panels, as well as on vacuum-insulated glass for maximum insulation.

WEIGHT REDUCTION THROUGH THIN GLASSThin glass technology is, in fact, now ready for se-ries production. As re-gards the relevant values of heat insulation (Ugva-lue), total energy transmit-tance (g value) and light transmission (tV), thin thermal glass has the same values as conventional triple-glazing and even exceeds those values. The Saint-Gobain Isolierglas -Center in Germany, for in-stance, has been producing 3-millimetre triple-glazing

Design principles to reduce the weight of insulating glass through the use of transparent plastic film or panels. Photo: ift Rosenheim

THERMAL TRIPLE

I G T E C H N O L O G Y

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looking at the glass. When asked about concerns that non-toughened thin glass may lead to a greater risk of breakage, Wolfgang Böttcher, Head of Tech-nical Marketing at Saint-Gobain Glass Solutions Germany, said that a cer-tain amount of experience with thin glass is indeed required in production, in logistics and on the part of windows manufacturers, but that this should not pose any problems. SGIC Climatop Light thermal glass can be used without toughening for dimen-sions up to 1.4 x 2.2 me-tres. Another pioneer in the use of thin thermal glass is the German manufacturer Energy Glas GmbH. The company has majored on thin glass engineering since 2013, featuring three ther-mally pre-tensioned thin panels (TBG plus and ESG units). Its two products have the following techni-cal specifications: Neutra-lux Advanced Light (3-2-3 structure): Weight: 20 kg/m2, Ug value: 0.5 W/m2K, light transmission: 73 per cent, g value: 52 per cent, Neutralux Ensolar Light (3-3-3 structure): Weight: 22.5 kg/m2, Ug value: 0.6 W/m2K, light transmis-sion: 74 per cent, g value: 65 per cent. These panels can be made with a struc-ture of 3 millimetres/2 millimetres/3 millimetres in TVG plus / ESG up to a size of 1.5 x 2.5 metres. For bigger dimensions the panels are made thicker to

as climatic stress has been calculated with sufficient accuracy in a given location, so that the structural stabi-lity of the glass meets the relevant requirements, then ‘lightweight’ thermal panels are a very good way to com-plement traditional triple glazing. Wolfgang Böttcher explains the reasons: “It va-ries from case to case what kind of dimensions can be realised and with what kind of panel thicknesses. The-re are instances where the proportions of thicker pa-nels are rather excessive and where it therefore makes sense to use thinner ones instead.” The Rosenheim Institute for Window En-gineering (ift Rosenheim) recently published a rese-arch report entitled “Area Weight of Thermal Mul-tiple Glazing”[1] (2013), showing methods, design principles and the limits of weight reduction through the use of thinner glass and transparent plastic panels and film. glasstec 2014 will feature a range of solutions whereby the glass industry is seeking to master future challenges in this segment of highly insulating thermal multiple glazing. The lea-

meet the relevant structural requirements. One of the benefits of using toughened glass, according to the company, is that the risk of breakage can be reduced to almost zero in both internal and external logistics and that the risk of injury is much lower in any post-installation bre-akage. Thanks to pre-ten-sioned thin glass units, the company’s thermal glazing is apparently far more re-sistant to thermal impact. Energy Glas GmbH sees no increased risk that the panels might buckle.

SENSIBLE ALTERNATIVE, BUT NOT SUITABLE EVERYWHERETriple glazing with thin pa-nels is a sensible alternative to conventional structures, but not a pat answer to all weight issues, as it is not sui-table for all thermal glass ap-plications. This applies both to ultra-large panels and for applications where the law specifies greater minimal thicknesses, e.g. for fall pro-tection purposes. Nonethe-less, thermal glass with thin panels can be used in a large number of cases. As long

units for quite a while now – since 2008. The two fun-ction glass units made by this company, SGIC Cli-matop N Light and SGIC Climatop Lux Light, are 25 per cent lighter than stan-dard thermal glass. Thanks to their low emission coa-tings, they reach Ug values between 0.8 W/m2K and 0.5 W/m2K, depending on the model. In its choice of material, the Saint-Gobain Iso-lierglas-Center decided against the use of thermally toughened glass. Although the hardening of the indi-vidual panels enables to achieve bigger dimensions, this does not apparently pose any problems. Clima-tic stress may lead to sub-stantial deformation, which has a detrimental effect on the edge seal and therefore shortens the useful life of thermal glass. Moreover, any deformation of large panels may cause distor-ted mirror images while

Thanks to the use of thin glass (structure shown here: 3 mm / 2 mm / 3 mm), it is possible to reduce the weight of thermal triple glazing by one third in many applications.

Vacuum-insulated glass has a Ug value of less than 0.5 W/m2K and excellent soundproofing qualities, despite its minimum total thickness. To prevent the two panels from collapsing under atmospheric pressure, spacers are inserted in the space between the two panels, which is less than 1 mm in thickness. They are only visible from a very close distance and do not affect transparency.

so far been conducted in Germany (VIG – vacuum-insulated glass[2] and Pro-VIG – production engine-ering for vacuum-insulated glass[3]). The consortium of companies and research institutions favours an edge sealing system using welded metal sheets. This solution is thought to have the gre-atest chances that the VIG edge seal as an element will withstand any potential strain over a period of 25 years or more. At the moment the consor-tium is working on suitable system engineering under a project called VIG-S. The purpose is to work towards a vacuum-tight and me-chanically robust edge seal that meets the requirements for industrial implemen-tation, so that a decision for realisation can then be made. Another project, Winsmart[4], which is cur-rently being conducted by European research institu-tions and companies, focu-ses on developing vacuum glass with a tin edge. The aim is readiness for series production, but the final results are likely to take at least another three years. If the two consortiums that operate in Europe achieve their aim of boosting the long-term stability of the edge seal for individual ele-ments, then vacuum-insula-ted glass can develop into a serious alternative to triple glazing and can in many cases help towards a reduc-tion of unit weights.

um-insulated glass reaches a Ug value of up to 0.3 W/m2K. However, due to the high thermal stress on the edge sealing systems that are used by the two Asian companies (i.e. the glass solder), these product so-lutions cannot be used as single panels, but only as hybrid solutions in an insu-lated glass structure, invol-ving a counter-panel. Mo-reover, both systems have visible evacuation valves. Some European compa-nies are working intensively on VIG solutions that do not need such valves and which can be used as sin-gle elements (i.e. without counter-panels), allowing variable use in conjunction with float glass, single-sheet safety glass and laminated safety glass, achieving a Ug value of 0.5 W/m2K. Two research projects have

The increased use of thermal triple glazing has placed a greater focus on the problem of weight, especially with large glazing units. Being extremely heavy, they can often only be installed with the help of technical assembly equipment. This photo shows the crawler crane Robby 900 Universal, made by the German company TGT GmbH. Photo: TGT Teupen

LITERATURE1. ift Rosenheim, “Forschungsbericht – Flächengewicht Mehrscheiben-Isolierglas” (Research Report: Area Weight of Thermal Multiple Glazing), published in March 2013, www.ift-rosenheim.de 2. Project “VIG – Vakuum-Isolierglas” (VIG Vacuum-Insulated Glass), www.vig-info.de 3. Project “ProVIG - Produktionstechniken für Vakuum-Isolierglas” (ProVIG – Production Engineering for Vacuum-Insulated Glass), www.vig-info.de 4. Project “Winsmart”, www.empa.ch

ding global trade fair for the glass industry will be held in Düsseldorf from 21 to 24 October. As well as presen-ting a wide range of con-structional glass, the interna-tional trade fair will provide a comprehensive overview of the latest production and finishing technologies as well as the entire spectrum of glass applications.

VACUUM INSULATED GLASS AS A COMPLEMENTARY PRODUCTOne alternative to thin glass and plastic film and panels is to use vacuum-insulated glass (VIG), which has a double-glazing structure and is barely 10 millime-tres thick and therefore very light. Both convection and thermal conductivity are virtually eliminated through the evacuation of air in the

space between the two pa-nels. This space is less than 1 millimetre wide. In com-bination with low-emission coating, this ensures excel-lent thermal insulation. To ensure that the high atmo-spheric pressure of 10 ton-nes per square metre does not cause the panels to col-lapse, barely visible spacers are placed between the two panels. Industrially manu-factured vacuum-insulated glass is already being made by two companies: Nip-pon Sheet Glass Co. in Ja-pan and Beijing Synergy Vacuum Glazing Techno-logy Co. Ltd. in China. The insulation values of NSG glass, however, are no more than either 1.2 or 1.1 W/m2K, depending on the model. This level can also be achieved with conventio-nal double-glazing. Beijing Synergy says that its vacu-